The chemistry of polishing typical piezoelectric materials such as quartz or langasite (La.sub.3 Ga.sub.5 SiO.sub.14) is complicated. For example, when diamond and aluminum oxide are used to "polish" quartz or langasite, both produce a damaged surface, and diamond produces more seriously damaged surfaces for the same particle size.
The phase transition of quartz at 573.degree. C. limits the processing temperatures one can use in the fabrication of quartz resonators. It also prevents the use of quartz crystals in high temperature environments as, for example, as sensors. Langasite is a promising new piezoelectric material that is similar to quartz in its acoustic behavior, but unlike quartz, it has no phase transition up to its melting point of 1470.degree. C. This may allow higher stabilities through higher temperature processing, and may also allow sensors for high-temperature environments, such as deep oil and gas wells.
Langasite's acoustic attenuation has been reported to be three to five times lower than that of quartz. This suggests that higher device Qs should be possible, however, the Qs of langasite resonators have been reported to be significantly lower than the Qs that can be achieved with quartz resonators of the same frequency. This discrepancy has been attributed to the lack of good polishing methods for langasite.